1. Field of the Invention
This invention relates to a restraint pretensioner. More particularly, the present invention relates to a restraint pretensioner with a deceleration mechanism.
2. Description of the Background Art
A wide variety of vehicles use passive-safety devices such as restraints and harnesses. These systems are especially important for fast moving vehicles. Restraint systems in fast moving vehicles must be capable of fast actuation in order to lessen the severity of potential undesirable events.
Fast moving vehicles can subject the occupants to large accelerations/decelerations during unexpected, undesirable events, such as a violent maneuver or a crash. These accelerations/decelerations can lead to large displacements of the occupant's body, which can result in the occupant's body or head contacting structure or objects within the vehicle. This can result in serious injuries or possibly death. Specially designed seats and restraint systems are typically used to restrain the occupant, however, excessive body displacement can still occur during the undesirable events due to the wide range of human body types and sizes.
Restraint systems include inertia reels that are designed to prevent movement of the body during normal operation of the vehicle—such as reaching with the arms and turning of the torso. The inertia reels are also designed to lock (preclude webbing payout from the housing) when large accelerations or decelerations are detected. This minimizes the displacement of the seated occupant's body to mitigate the potential for injury. Furthermore, the seated occupant is sometimes out of position or engaged in reaching or turning motions during the onset of an undesirable event.
Even a securely restrained occupant seated firmly against the seatbelt with the restraint and inertia reel functioning perfectly, can still experience significant displacement (depending upon the severity of the event) and be seriously injured. This displacement can be the result of initial slack of the wound restraint, the compaction of the webbing on the inertia reel shaft, and/or induced stretch of the webbing material. Such displacement of a wound webbing is known as “pack down” or “film spool.”
Over the years, various types of pretensioners have been developed to eliminate or minimize webbing displacement. One example is disclosed in U.S. Pat. No. 6,698,677 to Happ et al. The pretensioner includes a pivotal rack arm and a piston with an integral rack. The rack arm precludes the linear movement of the piston prior to the pretensioner being activated. After the pretensioner is activated, the rack arm restrains the piston by engaging a pocket within the bottom of the piston.
The device described in Happ '677 is intended to automatically retract the restraint webbing early in the event. By doing so, undesirable slack is removed and after the webbing is tightened, the occupant is held in the ideal upright seated posture, thereby minimizing the potential for serious injury. The device may be mounted directly to an existing inertia reel in the case of a retrofit, or configured as an integral feature of the inertia reel itself. Furthermore, the device is designed so that actuation will not injure the occupant it is intended to protect and ensure a safe exit from the vehicle after a crash. Also, non-crash, inadvertent actuation will not inhibit the occupant's ability to continue to safely operate the vehicle, which is particularly crucial in aviation applications.
Another example is illustrated in U.S. Pat. No. 6,155,512 to Specht et al. Specht '512 discloses a seat belt pretensioner that includes a piston-like drive member arranged in a glide tube. A drive means produces a propellant gas that drives the drive member. A movement transmitting system connects the drive member to the seat belt. A discharge system with a release or rupture element opens a discharge orifice in the drive member during a return movement of the drive member.
Some pretensioners, however, suffer from bounce back. This occurs when an internal piston rebounds after reaching the end of its stroke. Bounce back can have the undesirable result of the rack re-engaging an pinion gear or otherwise interfering with the proper operation of an interconnected inertial reel.